I remember I learned to use the most basic Sketch Up tools in just a few days, just via trial and error. A tip: do not download the pro version of Sketch Up but first the free version. Obviously if you were skilled on some CAD or even some graphical software (like Photoshop, Inkscape, Illustrator) the learning curve would be instantaneous, but if you feel fast with your computer skills it should not take much effort to learn the basics.
Maybe you can find some video tutorials which are a good way to learn for yourself if you google something like
Google Sketch Up courses.
I also liked to draw permaculture plans on Google Sketchup, but I got frustrated after a certain point because the program is very well suited and easy to use for drawing squares and square-like shapes, but extremely tedious when creating and interacting with round shapes and all that involves them, and for permaculture purposes it's usual to use more rounded shapes and not angular, etc. So I ended up using vectorial graphics software (the open source Inkscape), which are also difficult to master and you are forced to draw everything in bird's-eye view but I felt it was good enough. There it goes an example of a garden I was managing:
But as I mentioned, I also did some Sketch Up, but I find it more useful for buildings and much more complicated for landscapes or gardening. There it goes another example of what I did with my home:
So it all depends on what use you want to focus on, how many time you get to learn about the software you finally use, and about your overall vision and how abstract/realist you want it to get.